The present invention relates to a charge transfer type analog signal processing apparatus permitting series write-in and parallel read-out of analog signals.
Recently, it has been seen energetic development of charge transfer devices such as CCD (charge-coupled device) and BBD (bucket brigade device). The charge transfer devices can store an analog quantity temporarily. An analog signal is sampled and the amount of charge is produced which is proportional to the analog sample. The charge packets are shifted along the charge transfer device in response to transfer pulses. After the transfer, if potential with the storage level is applied to only the transfer electrodes at the signal charge storage sites, the signal charge packets are stored in the storage sites. Dark current charge due to thermal excitation carriers produced in the semiconductor is added to the signal charge packet stored in the storage site thereby to distort the signal. The amount of dark current charge depends on defects of a semiconductor substrate and the manufacturing process of the device. In the worst case, the amount of the dark current charge after 100 ms of storage time sometimes reaches about 1/3 of the maximum storable amount of signal charge in the storage site. Under this condition, it is impossible to store the signal charge for a long time.
The analog signal processing apparatus using the charge transfer device has found various uses. A transversal filter is enumerated for one of them. An analog signal processing apparatus for making the weighting signals for the transversal filter from an analog signal, for example, if desired for in which the analog signal is periodically written into the signal procesing apparatus and analog signal charge packets are read-out from charge storage sites in parallel fashion and then the signal charge packets read-out from one storage site are integrated.